My wife has a murano. We got the same letter. After digging around, it turns out that it is in response to the probability of a class action lawsuit.
Obviously, when the CVT fails the vehicle can't move when the accelerator is pressed. i.e. at a busy intersection, or railroad crossing.
The cost to replace it is also around 5k-6k.
Couple those factors and a class action lawsuit was coming down the pipe.
I'm glad, like you tony, because it's warrantied for another 50k. That said, I'll sell it before the warranty runs out.